A conventional known surface defect inspection apparatus includes a light projector that illuminates the surface of a target under inspection with light, a first light receiving unit that detects the amount light regularly reflected on the surface of the target, and a second light receiving unit that detects the amount of light irregularly reflected on the surface of the target. Japanese Laid-open Patent Publication No. 9-33446 is an example of related art.
If defective foreign matter with a predetermined height or more is present on a surface under inspection, when an inspection apparatus moves on the surface under inspection, the inspection apparatus may collide with the foreign matter and may be thereby damaged. Accordingly, it is desirable to check whether defective foreign matter with a predetermined height or more is present on the surface under inspection before the inspection apparatus is moved.
As with the above surface defect inspection apparatus, however, even if the amounts of light regularly and irregularly reflected on the surface under inspection can be measured, it may not be possible to check whether defective foreign matter with a predetermined height or more is present on the surface under inspection. In a case as well in which minute irregularities that may irregularly reflect light have been formed at a position, on the surface under inspection, onto which light is directed, a decision result may be affected by the irregularities.